pg: scram-sha-256 authentication fails (md5/trust work) — default auth on PostgreSQL 14+ #11336

Found by tokio lane L3 (#11331) with a live PostgreSQL 16.15 and pg 8.23.0. It reproduces on main.

Connecting with scram-sha-256 auth fails with "password authentication failed" under Perry, while Node connects with the same credentials. md5 and trust auth work.

Likely a crypto primitive used by SCRAM (pbkdf2 / HMAC-SHA-256 / saslprep / base64 of the client proof) differs from Node. scram-sha-256 is the default auth for PostgreSQL 14+, so this affects most real deployments.